1) Field of the Invention
The present invention relates to the attenuation of blasts and, in particular, to apparatuses and methods for attenuating blasts with a shield formed of attenuation, or absorptive, material.
2) Description of Related Art
An explosion is typically characterized by a blast or sharp increase in pressure that propagates in a wavelike manner outward from a point or area of origination. Whether intentionally or unintentionally initiated, such blasts can result in severe damage to buildings, vehicles, and personnel. For example, a blast from a bomb that is detonated in a car parked near a building can cause structural damage to the building, damage components therein, and/or injure people within the building. Similarly, ballistic and aerial explosive devices can cause costly damage to buildings and other types of structures. An explosion originating in a cargo container can rupture the container and propagate therefrom. Explosive blasts can also travel through media other than air, for example, an underwater blast that propagates to a boat, submarine, or other vessel and inflicts damage.
The use of barriers for attenuating the blasts associated with explosions is well known. For example, buildings at risk of blast damage during battle conditions are sometimes protected by walls formed of concrete, sand bags, and the like. Such dense barriers provide a protective effect to an area by deflecting and/or attenuating the blast and thereby preventing the blast from reaching the protected area or at least reducing the momentum or overpressure of the blast that does propagate to the area. In some cases, however, the blast may refract over or around the barrier and propagate into the protected area. Additionally, the construction of barrier devices can be prohibitively expensive, and such barriers can be impractical for protecting high structures, structures in densely populated regions, mobile structures, or underwater structures. Further, barriers can detract from the aesthetic appeal of a structure or area.
Thus, there exists a need for a blast attenuation device that provides an effective and space efficient shield for a protected area, including an area that includes a tall structure, a structure in a densely populated region, a mobile structure, or an underwater structure. The shield should be cost effective for construction, operation, and maintenance. Further, the shield should be adaptable to minimize the aesthetic impact of the shield or to render the shield aesthetically appealing.
The present invention provides a system and method for producing a shield for protecting an area. The shield provides an attenuation of a pressure blast, and can be used with tall, mobile, and underwater structures, including structures in densely populated areas.
According to one embodiment, the present invention provides a shielding system for attenuating a pressure blast to shield a protected area. The system includes a source for providing an attenuation material, i.e., an absorbing material, and a delivery system with a plurality of nozzles fluidly connected to the source by one or more passages. A valve device is configured to control the delivery of the attenuation material through the nozzles. The valve device can be actuated by a detector in response to a perceived blast threat, for example, an approach of a blast originator toward the protected area. In one embodiment, pipes are disposed at a peripheral area of a building, and the nozzles can be configured to direct the shield to extend substantially vertically and proximate to walls of the building.
The source can provide solid attenuation particulates, water or other liquids that the nozzles deliver as droplets, or a gas delivered as bubbles in a liquid medium. The attenuation material can be delivered as particulates having an average size of between about 0.01 mm and 1.0 mm, and the shield can have a three dimensional, or volumetric, packing factor of between about 0.001 and 0.01. According to one aspect, the packing factor is non-uniform across its thickness, for example, to generally increase in a direction from the origination toward the protected area.
According to another embodiment, the present invention provides a pressure attenuation shield for attenuating a pressure blast and shielding a structure. The shield is formed of one or more sprays of attenuation material that are disposed proximate a periphery of the structure and between an origination of the pressure blast and the structure so that the shield attenuates the pressure blast by at least about 14.7 psi within a thickness of less than about 1 meter of the spray. According to one aspect, the shield includes first and second generally parallel walls disposed between an origination of the pressure blast and a protected area. A flexible host material such as a gelatinous fluid is disposed in the space between the walls, and an attenuation material is disposed as particulates suspended in the host material. The attenuation material is configured to attenuate the pressure blast and thereby reduce the pressure blast to below a damage threshold of a protected article in the protected area. The shield can be configured to form a cargo container.
The present invention also provides a method of attenuating a pressure blast to shield a protected area. The method includes detecting a threat of a pressure blast and, in response to the threat, spraying particulates to form the shield between an origination of the pressure blast and the protected area so that the shield attenuates the pressure blast from the origination.
Further, the present invention provides a method of constructing the system for attenuating a pressure blast and mitigating blast damage to a structure. The method includes determining a maximum initial pressure against which the structure is to be protected, determining an acceptable pressure to which the structure may be subjected, and selecting an attenuation material comprised of particles having a desired radius, mass density, and three-dimensional packing factor. A minimum thickness is determined, for example, according to a mathematical expression, for a particle mist of the attenuation material required to reduce the initial pressure to the acceptable pressure. A delivery system is mounted to the exterior surface of the structure such that the system is capable of providing the particle mist at least as thick as the determined minimum thickness.